In some cases, a gas seal device is disposed in a rotary machine, such as a centrifugal compressor compressing a process gas as a fluid, so that leakage of the process gas to the outside of the machine is suppressed.
This gas seal device is disclosed in, for example, PTL 1.
Specifically, the gas seal device is disposed in a shaft end portion of a rotary shaft and is provided with a rotary ring and a stationary ring. The rotary ring is integrated with the rotary shaft in an outer peripheral portion of the rotary shaft, and the stationary ring is fixed to a casing and disposed to face the rotary ring in an axial direction of the rotary shaft. The stationary ring is pressed against the rotary ring by a spring. As a result, the stationary ring and the rotary ring collide with each other and a state where no gap is present is reached in a state where the rotary machine is stationary. Because a spiral-shaped groove is formed in a surface of the rotary ring that faces the stationary ring, a seal gas is introduced into the spiral-shaped groove once the rotary machine is put into operation and the rotary shaft rotates. Because of the pressure of this gas, the stationary ring is pressed along the axial direction of the rotary shaft against the biasing force of a coil spring, and then a minute gap is formed between the rotary ring and the stationary ring. Wear attributable to contact between the rotary ring and the stationary ring is suppressed by this gap, the amount of leakage of the seal gas from the gap is kept at its minimum, and the process gas is sealed in the rotary machine.
In some cases, the seal gas that is introduced into the gas seal device is generated by means of some of the process gas from the compressor. In this case, the process gas is passed through a filter, and then it becomes the seal gas by foreign matter being removed from the process gas. Depending on composition, the process gas is highly likely to be liquefied, and thus the temperature of the gas that has passed through the filter is raised by a heater, to at least a dew point temperature, in some cases.